Telecommunication systems using optical fibers need generally to be designed for the transmission of information in both directions, the end components serving therefore both for introducing into the fiber at least one signal from at least one emitter placed at the same end of the fiber, and for extracting therefrom and separating the signals originating from emitters placed at the other end. The various signals, in either direction, are of course carried by lights of different wavelengths, each generally occupying only a narrow band of wavelengths.
The end components are therefore traversed by lights differing in wavelengths and, above all, differing greatly in intensity. Thus the lights which are to enter the end of the fiber are very intense because they come from emitters placed at this same end of the fiber, while the various lights which are received are attenuated by extended travel in the fiber. Very different levels of intensity are also observed among the signals which are received, depending on the power of the emitters and or the transmission distance.
The receivers are designed to be capable of operation at very low optical levels in view of the normal attenuations in the transmission fibers, and are therefore particularly sensitive to any stray light originating, for example, from nearby emitters or even from other lights which are received and which have retained a higher intensity.
As a result, one and the same end component may need very different degrees of filtration, for example, to prevent the outputs to the receivers being perturbed by the reflected or diffused stray lights derived from the intense light from nearby emitters, to separate properly wavelengths having similar attenuation, or to segregate wavelengths which are difficult to filter. Most frequently, the greater the attenuation of a signal arriving at the end of a transmission fiber, the more complete must be the filtration of its wavelength band in the end component. Moreover, it can happen that the filtration of a particular wavelength must be specially improved on account of specific difficulties in filtering it with usual external means.
The present invention makes it possible to produce, in one and the same component, different degrees of filtration for different wavelengths or wavelength bands, and therefore permits better adaptation of the filtrations to the specific characteristics of the various wavelengths which are to be processed.